Correlate precise genetic control of immune responsiveness of inbred mouse strains to different murine oncornavirus gp70 determinants. Determine the relative contributions of humoral immunity and classical cell-mediated immunity by cytotoxic T lymphocytes in affording protection against well-defined tumor antigens and tumor growth. Induce tumors in appropriate parental strains with cloned, characterized N- and B-tropic oncornaviruses. Test these tumors for growth in F1 hybrids constructed between the parent of origin and appropriate H-2 haplotype partner. Study the following parameters of immunological responsiveness determining host resistance to tumors: serum antibodies and tumor specific T lymphocytes. Identify distinct members of the gp70 family to which lr gene controlled responses are directed.